Several such navigation systems have been proposed. For example, there is a system which recognizes, by viewing with a camera, a white line drawn on a roadway and navigates a vehicle along this white line. Also, there is another system which navigates a vehicle along a roadway by detecting a magnetic tape or magnetic line, or magnetic nails which are provided in a row along the roadway. All these systems employ one type or another of navigation- guiding mark including white line, magnetic tape, and magnetic nail; and vehicles navigate along the guiding mark by detecting it.
In this type of navigation system, as long as the guiding mark extends substantially straight or in a gentle curve, the detection of the guiding mark is relatively easy, so the control of navigation is relatively simple. However, if the guiding mark extends in an abrupt curve, or if it branches out, or if it merges with another, the detection or identification of the guiding mark or marks becomes difficult. If the system were to recognize such diversifications in the guiding mark, the design of the system would be complex, requiring a much higher cost for construction.
More specifically, the vehicle needs a device which can identify each of the ways where the roadway divides into two, or the roadway merges with another. This extra device requiring a high resolution sensor and an elaborate processing increases the manufacturing cost of the system. In addition, the roadways need to be provided with complex navigation-guiding marks to help the device identify the branching and merging of the roadways, which increases the cost for building the infrastructure necessary for the system.
Furthermore, as the direction of the vehicle comes to differ from the direction of the motion of the vehicle where the roadway curves abruptly, the sensor of the system is likely to miss the guiding mark.
As a result, the system becomes unable to track the route which is defined by the guiding mark. This is a serious problem which obliterates automatic navigation.